The present invention relates to the field of conical shaped cutting tools for the engraving and cnc machining industry.
Though many different shaped cutting tools are available that are capable of engraving or milling a thin line in a variety of materials, the most popular and effective cutting tool for producing thin lines is a half split conical shaped engraving tool with a single cutting edge. This tool is considered the “standard” in the engraving industry.
The standard conical shaped engraving tool that is used for engraving fine lines in material such as aluminum or stainless steel is typically created by splitting the end of the engraving tool in half with a grinding wheel, grinding the cone shape on the end of the tool, putting a relief on the cutting edge and then grinding a small angled flat tip on the end to generate the desired tip width which will create the engraved line. This tool is very effective at producing a clean engraved line in most materials. An example of this tool can be seen in FIG. 6 of Grenier U.S. Pat. No. 5,397,204 and in FIG. 8 of this application.
The production of the standard conical shaped engraving tool involves removing half of the material from the end of the tool which considerably weakens the tool tip. When engraving softer materials such as plastic or aluminum, this tool configuration is acceptable. When attempting to cut harder materials such as stainless steel, titanium or tough aerospace materials, the tips have a tendency to break off which renders the cutting tool useless and forces the user to replace the tool.
Tool designs other than the standard conical shaped engraving tool are available for cutting tougher materials but are not much more effective.
One tool that is often sold to engrave stainless steel is known as a quarter round engraving tool. This is simply a standard conical shaped engraving tool with a second split perpendicular to the first split. This has the effect of removing three quarters of the material from the tip of the tool. Although the tool has much greater clearance for the cut metal chips to be evacuated from the cut, which aids in reducing burrs on the surface of the material being engraved, the tip is very prone to breakage as is expected.
Antares, Inc. (Horsham, Pa.) developed a tool marketed as the Spiralflute® engraving tool. This is a conical shaped engraving tool which uses a right handed spiral drill like flute for the cutting edge instead of simply splitting the tool entirely in half. Since the tool has a cone shape, it is necessary for the flute to be ground all the way to the center axis of the tool so there is a cutting edge located on the tip. If the flute is not ground all the way to the center, there will not be any cutting edge located on the tip of the tool. The helical shaped cutting edge provides for a marginally stronger cutting edge than the standard conical shaped engraving tool but the tip of the tool still breaks off due to the fact that approximately half of the tool material is still being removed during grinding.
A pyramid shaped cutter can be seen in FIG. 8 of Richardson U.S. Pat. No. 4,448,120. This pyramid tool simply has multiple facets ground to a point on the end of the tool. There is no relief on the backside of the cutting edges so the tool doesn't actually cut or scoop any material from the workpiece while it is cutting but instead pushes a burr up during the cut. This burr is undesirable and produces a jagged looking line. Since there are no actual cutting edges on this tool, it has a tendency to chip easily and the tips break off.
Other tool designs are available that could be used for engraving. For example, Pantzar U.S. Pat. No. 5,971,670 describes a standard ball nose shaped endmill. Although this tool may be used to engrave a line, since the end of the tool has a full radius and is not conical shaped, as the tool is plunged deeper into the material, the width of the line increases very rapidly. If an extremely small diameter tool is used to attempt to engrave a fine line, the tools break very quickly because there are two opposing flutes cut into the tool and the diameter of the remaining material at the tip is very small. Cutting two flutes into the end of the tool removes a large amount of material from the very tip of the tool and weakens the tip making it prone to breakage.
Reynolds U.S. Pat. No. 6,095,723 describes another multiple fluted engraving tool. Reynolds invention's primary concern is that the tool should have two opposing flutes so the tool has two cutting edges instead of one like a standard half split engraving tool. Having two cutting edges allows operating the tool at a faster feedrate since the chipload on the cutting edge will be shared among the two flutes. However, looking at FIG. 3 of the Reynolds patent, it is obvious that a significant amount of the material has been removed from the tip of the tool and will therefore not be a strong tip design. It can also be seen from the same figure that with multiple fluted tools, the very tip of the tool comes to a sharp point where the two opposing flutes meet at the tip. This small point has almost zero material at the very tip where the multiple flutes meet. Additionally, when the tip of the tool comes to a point on the central rotating axis of the tool, the rotating surface speed of the tool at the tip is essentially equal to zero. For example, as the tool rotates around, the areas of the cutting edge that are located on the outer diameter are moving at a faster surface speed than the areas closer to the central axis. As you move closer to the center of the rotating axis, the surface speed is slower and when you reach the center of the tool it is essentially zero. Since the surface speed at the center is zero, there is no cutting action going on at the tip of the tool and there is a large amount of pressure applied to the tip as it is pushed through the material being engraved. This will quickly lead to tip failure of the tool.
Chen (Pub. No. US 2003/0059263) describes a multiple fluted tool similar to Reynolds. This tool is identical in configuration to standard chamfer tools that have been on the market for many years. The tool simply has multiple flutes cut to the tip of the tool. Chen describes shaping the overall end of the tool with different radii to produce machined lines that have different shapes at the bottom of the machined surface. Chen pays no attention whatsoever to the actual configuration of the tip. As with Reynolds, as the multiple flutes are cut to the tip of the tool, the opposing flutes meet at the tip on center and remove a large amount of material from the tip of the tool. Removing such a large amount of material from the tip of the tool significantly weakens the tip of the tool. Since the flutes are cut to the center of the tool, the very tip of the tool has a surface speed of zero as it rotates. As with Reynolds, this will provide for very poor cutting action at the tip and will apply a large amount of force to the tip. This will lead to breakage of the tip of the tool.
The present invention addresses this problem of tip breakage with a new unique design that removes a minimal amount of material from the tool tip which significantly increases the strength of the tool tip and overall life of the tool when cutting tougher materials such as stainless steel.